In ‘Peak Car Use’: Understanding the Demise of Automobile Dependence, published last month in World Transport Policy and Practice, Peter Newman and Jeff Kenworthy, of the Curtin University Sustainability Policy (CUSP) Institute in Australia, summarize recent data suggesting a long-term shift towards declining car use in cities in the United States, Australia and other developed nations. Growth rates in vehicle-miles traveled (VMT) in developed cities has been declining for decades. As an example, per capita VMT in cities they studied had climbed 42 percent between 1960 and 1970, but had slowed to 5 percent in the 1995 to 2005 period. Some American cities experienced a dramatic decline during thisperiod, with VMT in Atlanta and Houston declining by 10 and 15 percent, respectively.

Six possible factors may be driving this change:

Hitting the Marchetti Wall – Many cities have grown to the point where additional suburban expansion will cause their average commuting time to exceed one hour—the maximum amount of time that most people are willing to commute to work.

The growth of public transport – Transit ridership grew substantially during the 1995 to 2005 period in many U.S. and Australian cities.

Reversal of urban sprawl – Data suggests that the trend towards declining urban density has reversed and that more people are now moving into dense urban areas than are moving out.

Aging populations – The average age of urban residents has been increasing, which may contribute to declining VMT since older people tend to drive less.

The growth of a culture of urbanism – Both older “empty nesters” and young adults who have grown up in the suburbs are moving from car-dependent suburbs to cities.

Rising fuel prices – Fuel prices have been shown to impact suburban real estate values during past periods of oil price volatility. While in the past these impacts have been short-lived, a long-term increase in fuel prices will likely result in reduced demand for housing in car-dependent suburbs.

The implications of this shift for planners, transportation engineers, and others will be dramatic, likely including a more robust focus on multimodal mobility and urban design in the public realm and a shift towards increasing urban density and reduced parking and road capacity.